The system, devices, and methods under consideration relate to the drilling of a bore hole or well typically carried out using a steel pipe known as a drill string with a drill bit on the lowermost end. The entire drill string may be rotated using an over-ground drilling motor or the drill bit may be rotated independently of the drill string using a fluid powered motor or motors mounted in the drill string just above the drill bit. As drilling progresses, a flow of mud is used to carry the debris created by the drilling process out of the bore hole. Mud is pumped through an inlet line down the drill string to pass through the drill bit and returns to the surface via an annular space between the outer diameter of the drill string and the bore hole. Mud is a very broad drilling term, and in this context it is used to describe any fluid or fluid mixture used during drilling.
When drilling for oil or gas or other objectives, the drilling mud is used to lubricate the drill bit and pull cuttings up through the annular space. The mud and cuttings exit the well and are typically directed to a shaker to screen out the cuttings, and then to a further treatment step before the mud, minus contaminants, is returned to the bore hole. It is well known to monitor the flow of mud through the drilling system because it is important to the proper functioning of the drill bit and because unexpected changes in mud flow may indicate potentially dangerous conditions.
Current technologies that monitor mud flow have deficiencies. For example, Coriolis meters are unable to detect a stoppage of mud flow and have limitations related to reliability. Deflecting paddle systems have poor resolution and wear out quickly due to the abrasive quality of the mud and cuttings.